1. Field of the Invention
The present invention relates to methods for etching and galvanic production of electrically conducting or insulating ring zones in the interior of small diameter holes in a workpiece having a small thickness.
2. Description of the Prior Art
Gas discharge devices frequently employ a flat plasma screen of the type, for example, disclosed in U.S. Pat. No. 3,956,667 corresponding to German Pat. No. AS 24 12 869 wherein, for each picture point, the electron flow from the plasma chamber to the luminous material on the screen is regulated by means of an electrode matrix which is formed on a control disc or plate. The control plate is approximately the same size as the screen and consists of glass having a large number of holes or continuous perforations therein corresponding to the grid of picture points and which is coated on both sides with metal conductor paths. In order to avoid a high amount of charge at the inner walls of the holes, sometimes, the inner wall of the holes must be metallized and moreover the metallization must be interrupted within the hole for a short distance, determined by the depth of the hole, at a location approximately in the center of the hole so that the two sides of the control plate at no point are connected so as to be electrically conducting. Because of the fineness and large number of the perforations, production of such insulating ring zones is extremely difficult and represents a problem in the art.